Cardiac arrhythmia, such as atrial fibrillation, occurs when regions of cardiac tissue abnormally conduct electric signals to adjacent tissue, thereby disrupting the normal cardiac cycle and causing asynchronous rhythm. Important sources of undesired signals are located in various tissue regions in or near the heart, for example, the atria and/or and adjacent structures such as areas of the pulmonary veins, and left and right atrial appendages. Regardless of the sources, unwanted signals are conducted abnormally through heart tissue where they can initiate and/or maintain arrhythmia.
Procedures for treating arrhythmia include surgically disrupting the origin of the signals causing the arrhythmia, as well as disrupting the conducting pathways for such signals. More recently, it has been found that by mapping the electrical properties of the heart muscle in conjunction with the heart anatomy, and selectively ablating cardiac tissue by application of energy, it is possible to cease or modify the propagation of unwanted electrical signals from one portion of the heart to another. The ablation process destroys the unwanted electrical pathways by formation of non-conducting lesions.
A typical ablation procedure involves the insertion of a catheter having electrode(s) at its distal end into a heart chamber. An indifferent electrode is provided, generally adhered to the patient's skin. Radio frequency (RF) current is applied to the electrode(s), and flows between the surrounding media, i.e., blood and tissue and the indifferent electrode. The distribution of current depends on the amount of electrode surface in contact with the tissue, as compared to blood which has a higher conductivity than the tissue. Heating of the tissue occurs due to Joule heating. If the tissue is heated sufficiently, protein denaturation occurs; this in turn forms a lesion within the heart muscle which is electrically non-conductive.
A focal catheter works well, for example, when ablating a line of block in the atria. However, for tubular regions in or around the heart, this type of catheter is cumbersome, skill dependent, and time consuming. For example, when the line of block is to be made about a circumference of the tubular region, it is difficult to manipulate and control the distal end of a focal catheter so that it effectively ablates about the circumference. In current practice a line of block is accomplished by maneuvering the catheter from point to point and is highly dependent on the skill of the operator and can suffer from incomplete isolation of target areas such as the pulmonary vein ostia. However, done well, it can be very effective.
Catheters with circular ablation assemblies (or “lasso-type” catheters) are known. This type of catheter comprises a catheter body having at its distal end an ablation assembly with a preformed generally circular curve with an outer surface and being generally transverse to the axis of the catheter body. In this arrangement, the catheter has at least a portion of the outer circumference of the generally circular curve in contact with the inner circumference or ostium of a tubular region in or near the patient's heart, e.g., a pulmonary vein. However, one drawback with catheters of this type may be the relatively fixed size or circumference of the circular ablation assembly, which may not match the circumference of the tubular region undergoing treatment. Further, the variance in anatomy observed between subjects makes it difficult for a “one size fits all” approach.
Ablation catheters with inflatable assemblies or balloons are also known. Such balloons may include electrodes positioned on the outer surface of the balloons for ablating tissue and are typically inflated with a pressurized fluid source. More recently, inflatable catheter electrode assemblies have been constructed with flex circuits to provide the outer surface of the inflatable electrode assemblies with a multitude of very small electrodes. Examples of catheter balloon structures are described in U.S. application Ser. No. 14/578,807, titled Balloon for Ablation Around Pulmonary Vein, the entire content of which is incorporated herein by reference.
Flex circuits or flexible electronics involve a technology for assembling electronic circuits by mounting electronic devices on flexible plastic substrates, such as polyimide, Liquid Crystal Polymer (LCP), PEEK or transparent conductive polyester film (PET). Additionally, flex circuits can be screen printed silver circuits on polyester. Flexible printed circuits (FPC) are made with a photolithographic technology. An alternative way of making flexible foil circuits or flexible flat cables (FFCs) is laminating very thin (0.07 mm) copper strips in between two layers of PET. These PET layers, typically 0.05 mm thick, are coated with an adhesive which is thermosetting, and will be activated during the lamination process. Single-sided flexible circuits have a single conductor layer made of either a metal or conductive (metal filled) polymer on a flexible dielectric film. Component termination features are accessible only from one side. Holes may be formed in the base film to allow component leads to pass through for interconnection, normally by soldering.
However, where irrigation is desired or needed to cool and dilute the tissue region being ablated by an inflatable electrode assembly, perforation or the formation of irrigation apertures in a balloon membrane layer and an outer flex circuit substrate layer has posed numerous challenges. Where the apertures are formed in each layer separately, alignment of the apertures thereafter between the two layers has its difficulties. Where the apertures are formed in the two layers affixed to each other, methods for forming apertures in one layer may degrade or damage the other layer, especially where the two layers are constructed of material with different melting temperatures, such as Pellethane and polyimide. Patchworking the balloon structure with sections of perforated membrane and sections of perforated substrate can cause the balloon to misshapen, especially where the materials have different durometers.
Accordingly, a need exists for a method of constructing a catheter having an inflatable member or balloon with flex circuits and yet provides a plurality of irrigation apertures for irrigation of fluid from inside the balloon to outside. It is desirable that such method allows for the formation of irrigation apertures with uniformity and/or accuracy, without undesirable degradation or damage to the balloon membrane and flex circuit substrate, while enabling the balloon to maintain a desirable shape or configuration while inflated.